Polystyrene and polyurethane are the present front runners for preparing foamed products. However, these have many inherent disadvantages, i.e. high flammability, very little structural strength for self-support and for supporting fastening materials such as nails and screws.
Polyvinyl acetate polymer foamed products are known. However, these products are not readily found in the market place. The compositions of the prior art as disclosed in U.S. Pat. No. 2,930,770 do not satisfy the needs of the market place.
Our present invention provides a multipart composition which permits the effective use of polyvinyl polymers for foamed products. The polyvinyl polymers used in the present invention are always water-borne. The polyvinyl polymers of the present invention are those polymers and copolymers of polyvinyl acetate, acrylate, maleate and phthalate and also polyvinyl chloride and polyvinyl acetate-ethylene copolymers.
The preferred polymers used in the present invention are water emulsions of polyvinyl acetate and polyvinyl acetateethylene. These are usually used separately but may be mixed if desired. These chemical polymers are readily available and the polymers we used to illustrate our invention were Airflex 400, Airflex 300, Vinac 240 and Airflex 400H, which were purchased from Air Products and Chemicals, Inc. of Allentown, PA.
Airflex 400 and Airflex 400H are a water-based vinyl acetateethylene copolymer emulsion, which is 55% solids (Cenco Moisture Balance). The viscosity is 1400-1600 cps at 60 rpm (Brookfield Viscometer, Model LVF at 60 rpm and 77.degree. F.). The viscosity is 1900-2800 cps at 20 rpm (Brookfield Viscometer, Model RVF at 20 rpm and 77.degree. F.). The pH is 4.0-5.0. The residual monomer is 0.5% maximum. The copolymer type is vinyl acetate-ethylene. The protective colloid is partially acetylated polyvinyl alcohol. The density is 8.9 lbs. per gal.
Airflex 300 is similar to Airflex 400, except that the viscosity at 60 rpm is 1700 cps, and at 20 rpm is 2400 cps, and except that the density is 9.0 lbs. per gal.
Vinac 240 is similar to Airflex 400, except that the viscosity is 2700-3400 cps at 20-60 rpm, the pH is 4.5-6.0. Also, the polymer type is homopolymer, and the density is 8.9-9.2 lbs. per gal.
Also utilized were polyvinyl acetate water borne emulsions; namely, homopolymer adhesive base (standard), experimental 6-97 (homopolymer), experimental 6-124 (copolymer) and experimental 6-239 (copolymer). They were all purchased from Borden Chemical of St. Louis, MO.
The homopolymer adhesive base is a commercially available product, and the others are available for experimental purposes.
The commercially available adhesive base is 45% solids, and has a viscosity of 3500 cps at 60 rpm at 25.degree. C. The pH is 4.0-5.0. It is a homopolymer and has a density of 9.0.
The 6-97 homopolymer is 54% solids and has a viscosity of 3200 cps at 60 rpm at 25.degree. C. The pH is 4.0-5.0. the density is 9.0.
The 6-124 copolymer (blend) is 50% solids, and has a viscosity of 3500 cps at 60 rpm at 25.degree. C. The pH is 4.0-5.0 and has a density of 9.0.
The 6-239 copolymer (blend) is 58% solids and has a density of 9.1. The viscosity is 4000 cps and 60 rpm at 25.degree. C. and the Ph is 4.0-5.0.
In the four Borden Chemical polymers, the protective colloid is polyvinylalcohol.
As a blowing agent, we utilize natural and generally non-toxic blowing agents to provide a safe environment for foaming our products. The blowing agent we utilize is carbon dioxide. However, we obtain the carbon dioxide by reacting carbonates and bicarbonates with an appropriate acid. Further, as required by our invention, we use an alkali cross-linking agent. The preferred alkali compounds are Na, K, Li, Rb and Cs, although Mg, Ca, Sr, Ba and Zn can also be used. To effectively obtain both the alkali cross-linking agent and the blowing agent, we use the alkali carbonates and bicarbonates. The most common and readily available are ammonium bicarbonate, potassium bicarbonate, sodium bicarbonate, magnesium carbonate, calcium carbonate and zinc carbonate. Our preferred foaming agent is sodium bicarbonate.
Our invention requires our foam composition to also include and acid to release the carbon dioxide. However, in some cases the use of sodium bicarbonate alone is sufficient to release both the carbon dioxide blowing agent and to provide the alkali action as a cross-linking agent. The use of a cross-linking agent allows the foam product produced by our invention to have greater structural integrity than the foam products of the prior art. Our preferred acids are selected from citric acid, acetic acid, tartaric acid, hydrochloric acid and oleic acid. Of course mixtures of the acids and acid salts may be used. Our preferred salts are alkali bitartarates, monobasic calcium phosphate and monobasic sodium phosphate. Our preferred acid and acid salt are citric acid and potassium bitartarate, these both being readily available and, again, being non-toxic and thus environmentally safe for both the workers and the environment in the production of our foam products.
In addition to the above required compounds, other compounds may be utilized depending upon the end product to be produced. Those compounds which may be used may be suitable thickners, plastisizers, protective colloids, adhesives and various dyes. We have utilized and shown various additives such as carboxymethyl cellose, casein, polyvinyl alcohol, polyethylene glycol, starch, wheat gluten, dibutylphthalate, boric acid, gypsum, limestone, vermiculite, wood chips, popcorn chips and granules of popcorn.
The products produced by our invention show excellent flame resistance and stability. Wallboard produced with our composition had kraft paper on one side thereof. The wallboard may be used as a substitute for the present plaster board used in present wall construction. The wallboard produced by our intention allows screws to be screwed directly into the wallboard without the necessity of an anchor. Also, our wallboard has the same integrity as wood. That is, it will hold a nail in the same fashion that wood holds a nail. This, of course, is superior to the plaster board which is presently used in most construction. Further, our wallboard not only acts as a structural material, but also provides insulation and sound-proofing, which cannot be provided by plaster board.
Also, our composition can be used as a material, water based paint or coating, and an adhesive. The packing material is light weight and flame resistant, and thus has an advantage over known polystyrene packing materials.
Our paint or coating provides flame resistance and insulation.
The following examples more fully illustrate the invention, but it is not intended that the invention be limited to the exact procedures or concentrations utilized. Rather, it is intended that all equivalents obvious to those skilled in the art be included within the scope of the invention.
In all of the following examples the acid and carbonate blowing agent are added separately. Preferrably, the acid is first combined with polyvinyl emulsion. However, the manner in which the compositions are mixed is not important. They are mixed and agitated to cause the reaction to release the alkali cross linking action and the carbon dioxide blowing agent. When the acid, acid salt, and carbonate are solids they may be premixed and added as a unit. Also they may be suspended in a water miscible non-ionic liquid and added to the emulsion as a liquid.
The following Examples 13 through 28 use Borden's experimental 6-97 emulsion; Examples 29 through 32 use Borden's homopolymer adhesive base (standard) emulsion; Examples 36 through 52 use Air Products Airflex 400 emulsion.
As used in the examples PVA is polyvinyl acetate; H.sub.3 Ct is citric acid; KH Tar is potassium bitartrate; HAc is acetic acid and CMC is carboxymethyl cellulose.
In the following examples, it will be noted that by varying the formulation of the ingredients, various different properties of the resulting product can be emphasized. In this regard, density, structural strength, flame resistance and flexibility are the basic properties that are determined by the specific formuations of our composition.
In order to control the density, a low density is achieved by increasing the amount of the blowing agent. In this regard, an increase in the acid/carbonate ratio causes a decrease in the density correspondingly. For a higher density, the amount of the blowing agent is decreased, or the carbonates are increased.
Concerning the structural strength of the resulting product, in general, the higher density materials have better tensile and shear properties.
The flame resistance of the resulting product is better in the higher density resulting materials. In the higher density materials, increased carbonates cause better cross-linking and a better cell structure to occur, and thus the flame resistance is better.
Better flexibility is exhibited in the less dense resulting material. Also, for better flexibility, copolymers, plasticizers and CMC are used variously in the formulations. They are air dryed at room temperature. The more flexible materials may be used for packaging, due to the better cushioning properties.